I did a long weekend in brussels about 2 years ago jsut before christmas and I'd really recommend it. There were a large Christmas market on in the area, and we picked up some fab stuff at the stalls, hand made Christmas decorations, some lovely seasonal ceramics, and of course the manditory hot wine (vin chaud) and chips (frites).
We booked with priceline.com, and got the 4* Marriott hotel beside the european parliament for about Eu35 per night, as its a business hotel. Its a nice hotel, with pool but the area can be relatively quiet at the weekend. Its possible to make some brilliant savings with Priceline.com which can be spent elsewhere! It was about 10-15 min walk to Grand Place, where you will find a great range of restaurants.
My recommendation for a must do is to visit the Grand Sablon market on Sunday morning, its got some great antiques stands. When we visited there was a lovely cafe just opposite the church in that square that did a great sunday brunch, from memory lots of organic items on the menu.